University of Minnesota DISKCON USA 2006

Fabrication and Testing ofExchange Coupled Composite Media

Weikang Shen and Jian-Ping Wang

The Center for Micromagnetics and Information Technologies Electrical and Computer Engineering Department

University of Minnesota

Acknowledgement Acknowledgement

Dr. S. Y. Hong and Dr. H. J. Lee, Samsung Information Systems America Inc., for spin-stand testing.

Dr. S. N. Piramanayagam, Data Storage Institute, Singapore, for supplying disk substrates with soft underlayer.

Supported by INSIC-EHDR program and Heraeus Inc.

University of Minnesota DISKCON USA 2006

Outline

Introduction to ECC media

Fabrication of ECC media using CoCrPt-SiO2

Spin-stand recording performance of ECC media

Switching mechanism of ECC media

Conclusions

University of Minnesota DISKCON USA 2006

Exchange Coupled Composite Media for Perpendicular Magnetic Recording

Perpendicular magnetic recording (PMR) is currently replacing longitudinal magnetic recording.

However, the density limit of PMR is around 500 Gbit/in2:WritabilitySide track erasure (STE)Switching field distribution (SFD)

Kryder, et al, 2004

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Exchange coupled composite (ECC) media has been proposed and demonstrated to address above issues and extend the areal density of perpendicular recording.

Victora, et al IEEE Trans. Magn. 2005Wang, et al, Appl. Phys. Lett. 2005

Prototype ECC MediaSi(2 nm)/FeSiO(6.5 nm)/PdSi(t nm)/[Co/PdSiO]n(18.2 nm)/UL & SL/GL

0 20 40 60 80 1003000

4000

5000

6000

7000

8000

9000

Hcr (O

e)

Angle (Degree)

Hard Layer ECC

Remnant Coercivity (Hcr)

β= ΔHcr/H

ΔHcr

ΔHcr

β= 30%

β= 13%

0 1 2 3 43000

4000

5000

6000

7000

8000

9000

10000

tPdSi (nm)

Hc (O

e)

0

20

40

60

80

100

120

∆Ε/k

BT

ECC Media

Less angular dependenceSTE & SFD

Lower switching fieldWritability

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J. P. Wang, el al, Appl. Phys. Lett. 86, 142504(2005).

CoCrPt-SiO2 Hard Layer for ECC Media Si(2 nm)/CoCrPt-SiO2(20 nm)/Ru(40 nm)/Ta(5 nm)/Glass

Grain size: 7.0 nm

-10000 -5000 0 5000 10000-500-400-300-200-100

0100200300400500

M (e

mu/

cm3 )

H (Oe)

Hc 5.1 kOeMs 390 emu/cm3

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-10000 -5000 0 5000 10000

-600

-400

-200

0

200

400

600 Pt: 1.8 nm

M (e

mu/

cm3 )

H (Oe)

-10000 -5000 0 5000 10000

-600

-400

-200

0

200

400

600 Pt: 3.6 nm

M (e

mu/

cm3 )

H (Oe)

-10000 -5000 0 5000 10000-600

-400

-200

0

200

400

600Pt: 0.70 nm

M (e

mu/

cm3 )

H (Oe)

-10000 -5000 0 5000 10000

-600

-400

-200

0

200

400

600

M (e

mu/

cm3 )

H (Oe)

Pt: 2.0 nm

Perpendicular Hysteresis Loops of ECC MediaSi(2 nm)/CoCrPt-SiO2 (8 nm)/Pt(t nm)/CoCrPt-SiO2(20 nm)/Ru(40 nm)/Ta(5 nm)/Glass

Hsat

HsatHsat

Hsat

HHss~ Interlayer Thickness~ Interlayer Thickness

1 2 3 47000

7500

8000

8500

9000

9500

10000

Hs (O

e)

tPt (nm)

ECC media

Si(2 nm)/CoCrPt-SiO2 (8 nm)/Pt(t nm)/CoCrPt-SiO2(20 nm)/Ru(40 nm)/Ta(5 nm)/Glass

University of Minnesota DISKCON USA 2006

Disk Structures

Media Type Structures

ECC

Con. PMR

Ref. PMR N.A.

Si(1.5nm)/CoCrPt-SiO2(8nm)/Pt(1.0nm)/CoCrPt-SiO2(20nm)/Ru(20nm)/Ta(2.5nm)/SUL

Si(1.5nm)/CoCrPt-SiO2(20nm)/Ru(20nm)/Ta(2.5nm)/SUL

• After fabrication, all disks were packaged in the clean room and shipped to the company for post procession and spin-stand testing.

• Carbon overcoat was 3.5 nm thick. Lubricant is ~1.0 nm thick.• Reference PMR media is provided by a company, which is targeting for 200

Gbit/in2 areal density magnetic recording.

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Perpendicular Hysteresis Loops

-10000 -5000 0 5000 10000-600

-400

-200

0

200

400

600

M (e

mu/

cm3 )

H (Oe)-10000 -5000 0 5000 10000

-600

-400

-200

0

200

400

600

M (e

mu/

cm3 )

H (Oe)

Con. PMR (single hard layer) ECC media

Hc = 6.3 kOeHs = 12.5 kOe

Hc = 3.0 kOeHs = 7.0 kOe

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Spin-stand Test Results (1)

0 10 20 30 40 50 608

10

12

14

16

18

LF-T

AA

(mV

)

Write Current (mA)

ECC

Ref. PMR

Conv. PMR

Saturation CurveSaturation Curve

-20 -16 -12 -8 -4 0 4 8 12

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4 ECC Con. PMR Ref. PMR

Am

plitu

de (m

V/µ

A)

Write Offset(µin)

Track ProfileTrack Profile

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Spin-stand Test Results (2)

10 100 100050

60

70

80

90

100

110

Linear density: 584.4 kfci ECC Con. PMR Ref. PMR

Nor

mal

ized

Sig

nal (

%)

Time (Second)10 100 1000

50

60

70

80

90

100

110

Linear density: 52.8 kfci ECC Con. PMR Ref. PMR

Nor

mal

ized

Sin

gal (

%)

Time (Second)

HF-Time Decay LF-Time Decay

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Spin-stand Test Results (3)

0 10 20 30 40 50 608

10

12

14

16

18

LF-T

AA

(mV

)Write Current (mA)

ECC

Ref. PMR

Conv. PMR

Saturation CurveSaturation Curve

100 200 300 400 500 600 700 800 900

-20

-10

0

10

20

30 ECC Con. PMR Ref. PMR

SNR

_Tot

al (d

B)

Linear Density (kfci)

Roll-Curve

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Switching MechanismsSwitching Mechanisms

Incoherent SwitchingCoherent Switching

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Soft region

Hard region

Happ

Hex

Soft region

Hard region

CriteriaCriteria-- Exchange Length in the Soft LayerExchange Length in the Soft Layer

A Domain wall must fit in the soft layer near the switching point for exchange-spring model.

Domain Wall Width:

softappl

softsoftDW MH

A2≈l

A. Dobin and H. Richter, DB-10, Intermag 2006

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ECC Media Using [Co/ECC Media Using [Co/PdSiO]PdSiO]nn

Si(1.0 nm)/FeSiO(6.5 nm)/PdSi(t nm)/[Co/PdSiO]16(18.2 nm)/UL & SL/GL

0 1 2 3 4

4000

5000

6000

7000

8000

H

c (Oe)

tPdSi (nm)

ECC Media

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Domain Wall Width in FeSiO Domain Wall Width in FeSiO (M(Mss= 450 = 450 emu/c.cemu/c.c.).)

Domain Wall Width:

softappl

softsoftDW MH

A2≈l

A. Dobin and H. Richter, DB-10, Intermag 2006

Oe 194erg/cm 101

eum/cm 620

emu/cm 450

6

3

3

kHHA

M

M

cappl

FeSiO

CoreFeSiO

FeSiO

.≈=

×=

=

=

− nm 88.≈FeSiODWl nm) (6.5 FeSiOt>

University of Minnesota DISKCON USA 2006

A domain wall can not fit in 6.5 nm FeSiO (Ms= 450 emu/c.c.) at the coercivity point. Dynamic tilted switching (two spin-model) is the main mechanism for coercivity reduction.

Domain Wall Width in CoCrPtDomain Wall Width in CoCrPt--SiOSiO22(M(Mss= 800 = 800 emu/c.cemu/c.c.).)

Domain Wall Width:

softappl

softsoftDW MH

A2≈l

A. Dobin and H. Richter, DB-10, Intermag 2006

Oe 03erg/cm 101

emu/cm 950

emu/cm 800

6

3

3

kHHA

M

M

cappl

CoCrPt

CoreCoCrPt

CoCrPt

.≈=

×=

=

=

− nm 48.≈CoCrPt

DWl nm) (8.0 CoCrPtt~

A domain wall can fit in 8.0 nm CoCrPt-SiO2 soft layer at the coercivity point. Domain wall propagation (exchange-spring model) may be the main mechanism for coercivity reduction.

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Conclusions

Compared to conventional PMR media, ECC media showed an excellent saturation writing performance.

Disk level thermal stability was tested. No thermal degrading was found for ECC media, which confirmed the thermal stability of ECC media.

The switching mechanism of ECC media can be coherent switching or incoherent switching.

University of Minnesota DISKCON USA 2006